Well, I can think of a CSS hack that will resolve this issue.
You could add the following line in your CSS file:
* html .blog_list div.postbody img { width:75px; height: SpecifyHeightHere; }
The above code will only be seen by IE6. The aspect ratio won't be perfect, but you could make it look somewhat normal. If you really wanted to make it perfect, you would need to write some javascript that would read the original picture width, and set the ratio accordingly to specify a height.